1. Technical Field
The present invention relates to a light-emitting element, a light-emitting apparatus, a display, and an electronic device.
2. Related Art
Organic electroluminescence (EL) elements are light-emitting elements each composed of an anode, a cathode, and at least one light-emitting organic layer interposed between them. An electric field is applied between the cathode and the anode, electrons and holes are injected from the cathode and the anode, respectively, to the light-emitting layer where they are coupled once again forming excitons, and then the excitons return to the ground state emitting energy in the form of light.
An example of light-emitting elements is the one disclosed in Japanese Patent No. 3654909, a light-emitting element further having a hole-injection layer and a hole-transport layer interposed between an anode and a light-emitting layer in order for improved injection of holes.
Recently, there has been demand for improved properties of light-emitting elements (e.g., injection of electrons), and thus the elements often contain many layers other than those interposed between an anode and a light-emitting layer. In particular, white light-emitting elements require three light-emitting layers for emitting light in red, blue, and green colors, intermediate layers for balanced and/or long-lasting light emission, and many other layers, necessitating the use of too many layers for each light-emitting element. This problematically increases the driving voltage required to operate light-emitting elements.
The driving voltage requirement for light-emitting elements can be decreased by reducing the total thickness of layers interposed between an anode and a cathode. In a known light-emitting element, however, this allows foreign matter existing on the substrate to contaminate many of the constituent layers, resulting in a defective product with leakage between the anode and the cathode. So, the manufacturing of light-emitting elements has been facing the problem of low yield.